Transient energy transfer between writing beams during hologram formation in Bi 12GeO 20

Abstract

A large transient energy transfer between writing beams during volume phase-hologram formation in Bi 12GeO 20 has been observed. The variation of the energy transfer by applying an external field and by changing the fringe spacing of the elementary holograms have been measured and described in the framework of Kukhtarevs nonlinear theory of transient self-diffraction. The results indicate that the transient energy transfer in Bi 12GeO 20 is due to a non-stationary phase mismatch between the intensity- and refractive index grating caused by photoconductivity and that the transient energy transfer increases with increasing fringe spacing and increasing applied electric field. Up to ten-fold amplification of coherent beams has been measured, corresponding to an exponential gain of Г = 2 cm -1. A continuous energy transfer has been observed when the phase between recording beams was changed linearly with time during recording. It is shown that light is coherently amplified for electric field strengths larger than 2.3 kV/cm and that a peak amplification factor of Г 1 = 2 cm -1 has been reached for E 0 = 11 kV/cm.